Photodetectors have many industrial and commercial applications. For example, photodetectors can be configured as proximity sensors, which are used in various consumer electronic products for sensing positions and motions of users. Depending on the sense range, the application of proximity sensors can be broadly classified into two categories: short-range proximity sensors and long-range proximity sensors. A short-range proximity sensor, for instance, can be used in a hand-held device, such as a smart phone, for activating and deactivating a touch screen to avoid inadvertent inputs during a phone call. On the other hand, a long-range proximity sensor can be used in a video gaming system, such as a motion sensor, for detecting the relative motions of a user while ignoring the background.
A photodetector may be fabricated in an integrated circuit along with other circuits. The performance of a photodetector may depend on its ability to convert incident photons to a sense signal. A convergent lens (e.g., a convex lens) can be used to focus the incident photons for enhancing the performance of a photodetector. However, conventional convergent lenses are generally too costly to be fabricated alongside with a photodetector in an integrated circuit. Moreover, the installation of conventional convergent lenses may be incompatible with the fabrication process of an integrated circuit. Therefore, there is a need for an integrated solution for manufacturing a low-cost and high-performance photodetector within an integrated circuit.